Application of the Q-system to tunnels and caverns in weak or faulted rock

The frequent assumption of those who feel they know best is that the Q-system only applies to typical hard jointed rocks. A prominent critic has even unilaterally suggested limiting the range of application of the Q-value to what he has assumed is likely to apply. The above were not the intention of the developer who did the interpretation of the original case records in 1973 and could count 50 different rock types in the initial 212 case records. If a more limited range of application of Q had been suggested that would have been the result, since Q is an a posteriori empirical method. In this paper two examples of application of Q to cases outside the assumed reach of our critic are given. In both cases others had applied or were applying the Q-system when the writer joined or contributed to the projects concerned. One was a pumped storage cavern in Taiwan, the Mingtan Project with numerous (thirteen) clay-filled bedding-plane faults crossing the cavern axis. The other was the Channel Tunnel(s) between England and France driven by TBM in chalk marl with UCS of 4 to 7MPa. This rock was strong enough to be significantly jointed and cause serious over-break due to low Jr and high Jn especially in several sub-sea kilometres. It was originally not expected to be jointed, by designers. Hence the choice of this geology. As will be noted later, satisfactory design of support that resisted a very major earthquake was the result for the cavern, and concordant yet independent rock mass classification was the result for the chalk marl, which also explained overbreak problems for the TBM.